Due to the parity symmetry of the Lagrangian in Eq. (REF ), Eqs. (REF ), (REF ) and (REF ) give all the nonzero independent amplitudes for the process \(\mu ^-\mu ^+ \rightarrow \mu ^-\mu ^+\) , which can be used to yield the unitarity bounds on the 3-form field coupling to muons. Note that the unitarity of the S-matrix gives the following constraint [1]}, [2]}, [3]}, [4]} on the \(s\) -wave projected amplitude
\(\mbox{Re} (a_0) (\sqrt{s}) \leqslant \frac{1}{2}\,,\) 
